Electrical transformer



Dec. 11, 1928. 1,695,122

'C. F. PHILLIPS ELECTRICAL TRANSFORMER Filed Feb. 24, 1928 I4Noocoocoooisoouooqo.

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i v tallic I path whic Patented Dec 11, 1928.

urn-r1211 STATES aneua'r OFFICE.

ELECTRICAL TRANSFORMER.

Application filed February 24, 1928, Serial No. 256,748, and in Great Britain October 18, 1926.

This invention'relates to electrical transformers and particularly low frequency transformers used in wireless transmitting and receiving apparatus.

In smalltransformers of the type customarily used for low frequency coupling be tween thermionic valves it is well known that the primary winding is very subject vto breakdown. It is generally assumed that the breakdown is due either to vibration of the wire or to too great current density. Investigations I have made have proved however, that breakdown is due in most cases to electrolysis. As ordinarily connected in wireless receivin sets orgamplifiers the primary winding 0 the transformer is usually connected to the ing is usually connected to the negative pole of that battery either directly or through the battery used for heating the valve filaments. Assuming a high 'insulation resistance betweenthese primary and secondary windings it is clear that during the operation of the amplifier and also usually while the amplifier is not in use, the full potential of the high tension battery will be applied to the high insulation resistance between primary and secondary of the transformer and that a very small current will flow between them.

Owing to the impossibility in actual manufacture of entirely excluding moisture from the material separating the coils, and further owing to the fact it is commercially impracticable to obtain insulated wire entire a direct ath from coilto coil and the-other P age currents impossible, and my invention,

consists broadly in providing means where'- by theleakage currents leaving the higher potential windin ositive pole of the high tension battery w ile the secondary wind leaveentirely by a I term .an electmly tlc' shield and which is sufficiently substantial to withstand electrolytic action.

In order that the invention may be the more clearly understood ar number of intervalve transformers in accordance therewith will now be described reference being made to the accompanying diagrammatical drawings, Figures 1,2and 8, which illustrate respectively three of said transformers.

Thus in Figure 1 is illustrated a transformer comprising an iron core 1 a primary winding 2 and a secondary winding '3. In this case the electrolyticshield is constituted partly by a winding 4 located between the two transformer windings and partly by the iron core 1. The winding 4 may be nothing' more than a continuation] ofthe primary winding 2 which may be wound in the usual way in layers with insulating material between. Said winding 4 is however prefer-r ably of heavier gauge wire than that used for the primary itself.

The terminal P of the winding 2 is frequently adapted to be connected to the plate of a valve 'while the terminal marked is adapted to be connected to the high tension positive. The winding 4 and the core 1 are therefore both connected to said winding 2 at its end which is connected to said terminal The letter G and the sign respec- The transformer illustrated inFigure 2 differs from that of Figure 1 in that a nonmagnetic metallic cylinder 4, split to prevent the generation of eddy currents, takes the place of the coil 4. In this figure'moreover-the transformer windings are shown as made up of sections connected in series being wound, say, in a multi slot moulding in the well known way. I

The transformer of Figure 3 differs from thatof Figure 2 in that the sections of the rimarywinding instead of being wound in a multi slot former are wound on separate metal or metallized' bobbins 4 having side cheeks as indicated which bobbins take the place of the cylinder 4. These bobbins are insulated from one another and serve to connectthe several sections of the rimary winding as clearly shown in the rawing.

Like the'cylinder 4}. of Figure 2 these bobbins aresplit across to prevent the generation of currents. It will be clear that bobbins while forming the necessary electrolytic shield are so connected that the bobbins are of a progressively varying potential and thus the inherent capacity of the winding remains small.

In each example described the secondary has been shown inside and the primary outside. This arrangement may of course be reversed or I may use a split secondary with the primary in between. In this latter case the shield will of course have to have a part both inside and outside of the primary.

Further, in each of the examples described the core of the transformer has been described as connected to high tension positive so that said core forms part of the electrolytic shield. This of course is not essential and is only desirable in cases where it is reasonably robable that the electrolyzing current might otherwise pass fromthe primary winding to the secondary winding by way of the core.

I am aware that electrical transformers have been heretofore proposed having an electrostatic shield located between the primary and secondary windings and connected to one end of the latter.

What I claim and desire .to secure by Letters Patent is In an electrical transformer for use in radio receiving or transmitting apparatus with its primary winding connected to the positive, and its secondary winding to the negativepole of. the high tension battery, an electrolytic shieldconnected to said primary winding, said primary winding being wound in sections, each section being surrounded on its sides adjacent other sections and adjacent the secondary by a section-of the said shield, said shield sections beingeach connected to a section of the primary.

In witness whereof I afiix my signature.

CHARLES FRANCIS PHILLIPS. 

